Bend it like...HP

By Patrick Marshall

Jan 12, 2009

It’s been a holy grail for display manufacturers for years — the creation of flexible, bendable, foldable, rollable digital paper. Just imagine being able to take a folded sheet out of your pocket, unfold it and lay it on the table and — voila! — you’ve got a computer display. Or think of such a display sewn into the arm of your jacket so that you can check a map while you’re trekking an unfamiliar city.

Researchers at Arizona State University’s Flexible Display Center have taken a step closer to the development of a thin flexible display that might earn the name of digital paper. On Dec. 8, 2008, FDC researchers announced the first prototype of what they described as an affordable, flexible electronic display. Proponents say mass production of flexible displays could lower the price of laptop PCs, smart phones and other devices, because the displays currently make up a large part of their production costs.

The prototype displays were created using Hewlett- Packard’s self-aligned imprint lithography (SAIL) technology. To create the display, the FDC produced stacks of semiconductor materials and metals on flexible Teonex polyethylene naphthalate substrates from DuPont Teijin Films. HP then patterned the substrates using the SAIL process and subsequently integrated E Ink’s Vizplex imaging film to produce an actively addressed flexible display on plastic.

The result is a sheet about 350 microns in thickness. “That’s maybe a little thicker than a typical sheet of paper but not much more,” said Greg Raupp, FDC’s founding director.

Raupp said low temperatures and fewer steps make the new process special. “It’s essentially the same semiconductor technology as is used in glass displays, with the exception that we produce it at much lower temperatures,” he said. Higher temperatures would melt the plastic. Thinfilm transistor displays, for example, are produced at temperatures between 300 and 380 degrees Celsius. However, “because we fabricate on plastic,” Raupp said, “our temperature limitations are probably something on the order of 200 centigrade maximum.”

HP’s SAIL process allows for fewer steps in the lithographic process. “Anything from four to seven photolithographic graphic alignment steps must be done to make your fully functional TFT arrays,” Raupp said. “With the HP process, a large number of those photo lithographic steps are totally eliminated.”

Raupp said he expects that the first products to emerge will likely be electronic reader applications. “A next big opportunity from my perspective is in the wearable display,” Raupp said. “As a skier, I’m quite excited about the idea of buying a ski jacket that has a built-in flexible display in the sleeve. The technology really frees up product developers from the constraints of rigid glass,” he said. “Once I have the ability to put a display on any surface I’m going to start to think of ways I’m going to access and deliver information and entertainment in ways we really don’t do today.”

For now, the major hurdle ahead is to move from monochrome displays to full-color displays. The current flexible display technologies are limited to monochrome. Raupp said organic LEDs hold some promise for the future, but their sensitivity to environmental conditions requires them to be sealed in glass rather than the more permeable plastic layers of flexible displays. “We need a hermetic seal that is also flexible,” he said. “That today is a big technology gap.”